The objectives of this study are to determine the range of values for Lutenizing Hormone(LH), Follicle Stimulating Hormone (FSH), corticosterone, estrogen and testosterone in the plasma; and to describe the testicular, ovarian, and adrenal histology of Prairie Deermice (Peromyscus maniculatus bairdii) that are reproductively inhibited as a result of density dependent population factors. We shall measure the same parameters in control deermice that are maintained as bisexual pairs. During the growth of the experimental populations, measurements of births, survival, and the reproductive condition of all animals will be made during periodic inspections. The endocrinological parameters obtained for each population at sacrifice will be compared to those obtained for controls as well as analyzed relative to known behavioral and reproductive characteristics.